Exposure of right cavernous sinus, inner and middle ear structures, and roof of infratemporal fossa. The cerebrum has been dissected away to expose the brainstem and cerebellum in situ. The dura mater has been stripped from the lateral surface of the sphenoid body and greater wing and a portion of the greater wing and petrous temporal bone has been drilled. In this process, the lateral wall of the cavernous sinus has been exposed containing the oculomotor and trochlear nerves in its superior portion and the cavernous segment of the internal carotid artery. The right oculomotor (CNIII) nerve leaves the ventral midbrain while the trochlear (CNIV) nerve leaves its dorsal surface of the midbrain. Both nerves enter the orbit via the superior orbital fissure. The trigeminal nerve leaves the lateral surface of the pons and crosses the apex of the petrous bone where it then expands as the trigeminal ganglion. The ganglion lies in Meckel's cave on the trigeminal depression anteromedial to the trigeminal prominence, an elevation on the petrous ridge.  From this sensory ganglion arise its three divisions: ophthalmic (CNV1), maxillary (CNV2), and mandibular (CNV3) coursing toward their openings of exit; superior orbital fissure, foramen rotundum, and foramen ovale, respectively. Posterolateral to the foramen ovale is the foramen spinosum. The middle meningeal artery can be seen emerging from it. Posterolateral to the trigeminal prominence, the roof of the internal auditory canal has been drilled to expose the facial and vestibulocochlear nerves, as well as the bony labyrinth. The distal end of the auditory canal separates the cochlea, anteriorly, from the bony labyrinth and semicircular canals, posteriorly. In this view, the geniculate ganglion is exposed at the distal end of the canal. Here, the facial nerve continues posteriorly in the facial canal along the medial wall of the tympanic cavity inferior to the lateral semicircular canal and the greater superficial petrosal nerve takes its origin anteriorly from the ganglion. The greater superficial petrosal nerve leaves the anterior surface of the petrous bone through a hiatus and passes deep to the mandibular nerve toward the foramen lacerum and pterygoid canal to unite with the deep petrosal nerve to form Vidian nerve. The thin roof of the tympanic cavity (tegmen tympani) has also been drilled away to reveal the middle ear cavity. The anterior wall of the tympanic cavity has been opened to reveal two canals, one above the other. The superior of the two contains the tensor tympani muscle and the lower one is the bony part of the Eustachian tube. The tensor tendon curves sharply laterally to attach to the upper part of the handle of the malleus. The bone covering the roof of the infratemporal fossa has been drilled to reveal the superior head of the lateral pterygoid muscle and branches of the mandibular nerve. The mandibular nerve divides into a smaller anterior trunk or division that provides motor branches to the muscles of mastication and the sensory buccal nerve to the cheek. A larger posterior trunk or division gives rise to motor fibers to the mylohyoid and anterior digastric muscles and sensory fibers to the auriculotemporal, lingual, and inferior alveolar nerves. The tentorium has been incised to expose part of the rostral cerebellum. This surface is supplied by the medial and lateral branches of the superior cerebellar arteries that course posteriorly in the pontomesencephalic sulcus above the superior cerebellar peduncles before ramifying. The superior petrosal sinus is exposed in the tentorial attachment to the petrous ridge. It drains the cavernous sinus to the transverse sinus. (Image courtesy of PA Rubino)